The club are facing a transfer embargo over their bitter contract dispute with former winger Cameron Stewart.
United are accused of failing to pay money owed to the 24-year-old after they pulled out of a deal to sign him last season.
Leeds have so far refused to comment.
But the PFA are set to ask the Football League to prevent them signing players this summer if they do not meet costs of around £800,000 awarded to Stewart after a hearing in May.
Stewart, now at Ipswich Town, is claiming loss of earnings and the difference between his salary at Leeds and the wages he is now on with the Suffolk club.
He moved to Elland Road on an emergency loan from Hull City midway through last season. His contract was with a view to a permanent three-year deal.
The Football League, however, returned the signed paperwork to Leeds after problems were flagged up with it.
Former managing director David Haigh had signed the contract, but as he had left the club in April he was therefore no longer registered as an ‘authorised signatory’.
Instead of re-signing the contract, Leeds' new owner Massimo Cellino pulled the plug on the deal.